Undifferentiated NG108-15 neuroblastoma-glioma hybrid cells or NS20-Y neuroblastoma cells can be shifted to a differentiated state by increasing levels of cellular cAMP for several days. cDNA libraries were constructed for species of mRNA that increase in abundance during differentiation. Elevation of cAMP levels of NG108-15 cells for several days results in the expression of new glycoproteins, the disappearance of others, changes in the apparent abundance of some glycoproteins and shifts in the pI of some glycoproteins. The abundance of a voltage-sensitive calcium channel glycoprotein increases during differentiation. A large NG108-15 cDNA library was constructed in Lambdagtll, for use in cloning cDNA for choline acetyltransferase. A monoclonal antibody that recognizes a plasma membrane protein in chick retina cells that is distributed in a dorsal-ventral gradient in retina was injected into chick embryos in ovo. A marked reduction in synapses and neurites in the inner synaptic layer of the retina was observed. cDNA was synthesized from 14 day chick embryo retina RNA and cloned in Lambdagtll for use in cloning cDNA for the gradient protein. Many monoclonal antibodies were obtained that recognize antigens in the developing nervous system and some of the antigens were characterized. Several antibodies recognize novel gangliosides. A protein was purified from bovine brain that induces neurite outgrowth at nM concentrations and stimulates the phosphorylation of proteins in the absence of Ca2+ or cAMP.